1. Technical Field
This invention relates generally to a timing tool for measuring and setting the timing of fuel injectors and more particularly to such a tool for measuring and setting plunger position and travel of unit fuel injectors.
2. Background Art
Injection timing is a critical parameter for meeting emission standards on all diesel engines, including those used in locomotive and marine engines. Exact timing of the injectors is important because retarding the injection timing can reduce NOx emissions. However, if the injection timing is retarded beyond a target value, smoke emissions can increase above acceptable limits and the fuel consumption penalty can be excessive.
On many diesel engines, such as the General Motors Electro-Motive Division (EMD) engines, the fuel injection pump and spray nozzle are combined in a single compact unit called a unit injector. Unit injectors meter, atomize, and spray fuel into an associated cylinder of the engine. The pumping function of the injector is accomplished by the reciprocating motion of a constant stroke injection plunger which is actuated by an injector cam on the engine camshaft through an injector rocker arm. In the EMD engine unit injectors, the position of the plunger, and thereby the timing, is adjusted by means of a ball stud and lock nut at the injector actuating end of the rocker arm. The quantity of the fuel injected into each cylinder is varied by rotating the plunger mechanically by means of an injector control rack, or by electronically controlled valves. The plunger stroke remains constant at about ¾ of an inch.
The standard injection timing tool used for setting the injection timing in General Motors EMD engines is used to check the height of the injector plunger as the flywheel is set at a predetermined position. The tool has a steel shaft having a knurled end by which the tool is gripped. An end of the shaft opposite the knurled end has a narrow section that is inserted into a hole in the injector body. At the top of the narrow section, there is a step that acts as a stop to control extension of the tool into the hole so that the step rests directly on the top of the injector body. Above this step there is a larger shoulder that is adapted to be seated on a retainer element of the injector, and is spaced a predetermined distance from the step, for example 2.430 inches. It is this fixed distance between the step and the shoulder that allows the tool to be used as a feeler-type gauge for timing adjustment. The stock timing tool must be held in precise vertical alignment and requires considerable experience and a good sense of “feel” to achieve accurate and repeatable injector timing settings.
Injector timing tools have been developed for measuring injector plunger height on engines in which injector plunger position is controlled by an adjustable push rod connected to an end of the rocker arm opposite the plunger actuator end of the rocker arm. For example, U.S. Pat. No. 4,503,619 issued Mar. 12, 1985 to Nelsen, et al. for an INJECTOR HEIGHT MEASURING TOOL ASSEMBLY describes such a tool. However, the Nelsen, et al. timing tool cannot be used on rocker arm/injector arrangements that have the plunger adjustment means at the plunger actuator end of the rocker arm. For example, an adjustable ball stud mounted in the plunger actuator end of the rocker arm and an associated lock nut are used in the aforementioned EMD series diesel engines. This arrangement requires direct tool access to the ball stud and lock nut for adjustment of injector timing, a requirement prohibited by the Nelsen et al. timing tool which covers the plunger actuator end of the rocker arm.
The present invention is directed to overcoming the problems set forth above. It is desirable to have a fuel injector timing tool that does not require subjective “feel” and critical alignment to measure and set injector plunger position. It is also desirable to have such a tool that allows access to plunger position adjustment components mounted in the plunger activator end of the rocker arm.